Ignoring an Inconvenient Colorado River Basin Risk

Ringside seats to the decline of Lake Mead

Sometimes all we can do is sit and watch and wonder

By John Fleck

It is agonizing to watch this, but here we are.

With efforts by the Colorado River Basin states to craft an agreement to share the river’s water skidding, brakes screeching, toward a cliff, we appear on the brink of repeating the disastrous mistake the authors of the Colorado River Compact made a century ago: ignoring inconvenient truths about the risks we face, washing away genuine uncertainties with convenient talking points.

As Eric Kuhn carefully documented in a post here yesterday, there is once again a genuine risk that we will ignore inconvenient truths about a huge uncertainty in our understanding of how much water the river can offer us, and for whom. We are pretending that an uncertainty literally at the scale of millions of acre feet in how we measure and manage water does not exist.

A masterful Upper Colorado River Basin public relations blitz, led by the Colorado Water Conservation Board, would have us believe one set of numbers about the river’s future, a set of numbers that has given Upper Basin water users comfort that they can sit tight and blame others for the river’s woes.

But as Eric’s analysis showed, there are hidden assumptions behind the Upper Basin’s numbers – assumptions that hide a genuine and irreducible uncertainty. The uncertainty is irreducible because more than a century after the adoption of the Colorado River Compact, there is still no agreed upon definition of how to measure the use of water. As Eric wrote, these are questions “with enormous potential impacts on the allocation and distribution of the shrinking Colorado River – questions we have avoided dealing with by draining the Basin’s reservoirs. We no longer have that option.”

Arithmetic and Law

Eric is a master of the arcane and wonky details of the interface between Colorado River law and hydrology, and I commend you to his analysis – it rewards a careful read. But Eric once described my role in our collaboration as “dewonkifying”, so let me try to put this in simpler terms.

The 1922 Colorado River Compact based its allocations on “beneficial consumptive use”. But the phrase was never defined, and the definitions ended up bitterly contested in the decades that followed. It remains undefined to this day. Or rather, there are two competing definitions that yield very different results.

Each definition makes intuitive sense, and at first glance they look puzzlingly similar. But at the scale of the Colorado River Basin they yield very different results that have become a critical piece of the current basin management debate.

Method A is based on the collective amount of water communities take from the river, minus the amount they return – “diversions less return flows.”

Method B is based on the ultimate impact of that use on the Colorado River downstream of the use – for the Upper Basin, for example, at Lee Ferry, or for Arizona at the confluence of the Gila and the Colorado near Yuma. This is the “stream depletion theory”.

Those might sound so similar that the differences are trivial. And at localized scales they are. But, as Eric explained in yesterday’s post, with a classically Eric Kuhn working out of the mathematical details (I love collaborating with this guy – he shows his work!) at the scale of the Lower Colorado River Basin the differences amount to nearly 2 million acre feet of water.

Under Method A, Lower Basin use is more than 10.1 million acre feet per year, well above its Colorado River Compact allocation of 8.5 million acre feet. This is the methodology the Colorado Water Conservation Board staff used in its now-famous PowerPoint slide purporting to demonstrate that the  Lower Basin is using more than its legally allotted share of the Colorado.

But under Method B, Lower Basin use is some 8.3 million acre feet – less than its Compact allocation. Importantly, Method B is the method adopted by the Upper Basin Compact, and therefore the method used in the Upper Basin’s management of its share of the river.

Let’s Be Honest About the Uncertainties

To be clear, Eric and I are not arguing in favor of A or B. We are arguing, as we did in our book Science be Dammed (we spent chunks of three chapters on this question), that the lack of an agreement over the definition of “beneficial consumptive use” remains a genuine and important unresolved uncertainty in the Law of the River, and our discussions of the future management of the Colorado River need to acknowledge that uncertainty, not pretend that it does not exist.

This is what I, as a stakeholder whose community depends on the Colorado River, expect of those leading the interstate effort – public honesty about the genuine risks and uncertainties we face.



  1. Method A is the correct one. The fundamental law of hydrology is (Water in = Water out + or – change in storage) .That is it.

    I refer you to Section 5 of Konoplyantsev, A.A., Ineson, J., and Kovalevsky, V.S. 1972, Ground=Water Studies, Published by UNESCO, ISBN 92030100960-5

    This is an exhaustive treatment of the Water Balance. I have not found any copies for sale but a search of Worldcat.org shows a copy at the Univ. of New Mexico Library (Probably Centennial Library)

    University Libraries, MSC05 3020, 1 University of New Mexico, Albuquerque, NM, 87131, United States

    The thought that the LBS suffers under delivery of 8.1-million-acre feet is ludicrous. Method B is just hocus pocus.

  2. I think you have it backwards. Method A is the Lower Basin accounting method which ignores evaporation in reservoirs and transit loss on the rivers which is why their usage numbers are lower. They only count water that goes into their point of diversion. Upper Basin inflow/outflow accounting charges Upper Basin states with evaporation and transit loss. Lees Ferry gage inherently does too. Losses on CRSP reservoirs like Lake Powell and Flaming Gorge are explicitly charged to the Upper Basin, maybe 500,000 af/yr.

  3. The only opinion that I can add here is saying that there are no ‘absolute numbers’ in the amount of water in the Colorado River or any other water basin I can think of. The only absolute numbers are the ones that the politicians and lawyers have come up with. The numbers that we work with – how much water comes into the system due to precipitation? How much water is lost due to evaporation, transit and vegetation losses on the river channels is estimated on limited data. The term is ‘estimation’ and not a hard figure. The uncertainty of the estimate can be reduced with more comprehensive measuring but at what cost?

    I see the argument about what is used in the Gila River within Arizona. Why not measure the output of the Gila at the New Mexico – Arizona border and where the Gila dumps out at the Colorado River. Use the SAME gaging equipment types at both sites…No…Use the exact gaging equipment that is used at Lee’s Ferry Gage. As I remember, the USGS uses an Acoustic AVM to do the measurements at Lee’s Ferry.

    For those who do not know the accuracy of the technology, for this AVM the accuracy is 5.0%. This is the best accuracy using the state of the art equipment that can be used in an open channel under stable conditions. The water velocities measured off the AVM factored with the water levels in the channel (+/- 0.01ft accuracy) determine the flow. Other factors in the equation is based on the stability of inflows in the river where the measurement is made. Glen Canyon Dam is a few miles upriver and the flows are unstable due to Generators coming online and offline as the Grid Load changes.

    Do you guys see what I mean about ‘absolute numbers’ here? They exist on paper but are elusive in the real world. How do you explain this to somebody that crunches numbers in accounting or in the academic sector that doesn’t see it in the numbers? You can see (when in the field) slight abnormalities that are not revealed in the collection due to insufficient resolution. The assumption is made that the numbers are perfect. They aren’t

    I remember a conversation we had within the Agency. Maybe about twenty years ago. We were arguing just where the ‘accuracy’ in the flow readings were in the river. Was it more accurate in the Penstocks at the Dams or in the open channels of the river? My argument was the accuracy was at the Dams as the technology and sensing methods rendered 0.005% accuracy. The penstocks were fixed as the dimensions never changed (we knew the cross section measurements to the one hundredth of an inch). Nor, did the area of the water within the Penstock change.

    When measuring within the river channel, the open channels in the river were not fixed and the cross sections changed over time due to the bottom moving. Yet the field hydrologists argued the Dam’s flows were consistently less than what they came up with.

    Yes…True…We can’t account for water bypassing a Dam due to leakage. It was especially true in the case of earth filled structures. Another example of there are ‘no absolute numbers’ in collected Data.

    I can tell you that with my experience in collecting data from the Colorado River is that the more detailed data that you can collect from the river from higher time series resolution, the more you see. It’s better (but not absolute). That doesn’t exist.

    My recommendation is to collect data across the basin using the same methods and using the same equipment. The results will be more consistent. Unfortunately, it will cost more money.

  4. This posting does not exactly follow suit to those of John Fleck and Eric Kuhn, so please bear with me.
    I am reading a lot about the Colorado River water apportionment issue. My efforts are a work in progress in absorbing the writings of numerous authors including Fleck, Reisner, Gleick, Boyle, et. al. So far I’ve decided it’s one of the most convoluted issues I’ve ever tried to grasp. Full transparency, I live in Washington State and our water resources appear to be manageable in the least case while still we have some issues WRT dams, preserving salmon runs, and more. Nobody asked me, but I wonder how we get some “adult supervision” in the Colorado River business and seek lasting resolution to apportionment. Does the Bureau of Reclamation take charge–if not now then when? Does our President totally federalize the matter? I can’t imagine how the Upper Basin and Lower Basin stakeholders are going to find resolve while maintaining mutual respect. I’ve seen the quote “water is worth fighting for” but do we want merely to fight over it, allowing opportunity to slip away, or do we fix the problem?

  5. That set of authors probably doesn’t capture the events of the last twenty years. The pivotal event was AZ and SNWA threatening litigation in 2005 unless they got more water from Lake Powell, 9 MAF releases in key situations. Other states caved to avoid conflict and litigation. This delayed anyone taking shortages until recently when reservoirs were on the brink of collapse. Arizona’s team wrote a detailed law review paper describing what they did and why in 2007:

  6. Someone has to say it: while everyone argues about how to share the declining flows of the Colorado River, the basin states fail to even think about working together in an aggressive manner to halt the decline in flows. That is, work together – on behalf of the river – to halt climate change. That would mean a bipartisan effort in the basin states to aggressively cut greenhouse gas emissions by replacing fossil fuels with renewable energy and storage. All the tech needed is now available. And then, the states and their bipartisan Congressional delegations need to step up and demand more climate action at the national scale. They’d have plenty of allies, and would make a huge difference. The basin states don’t have large fossil fuel interests, and they do have plenty of sun and wind. And they do have a river that is relentlessly flowing less and less as the planet warms.

  7. Follow the Laws of the River. The Laws are there. Division # 6 follows all the laws. The other divisions need to follow the laws. Measuring devices and etc. If the Lower Basin has to have water cuts then the Upper Basin must have water cuts as well . All are Equal. Pay the people for their water. And follow the laws for Sr. water rights. The Government has to get involved. Bureau of Reclamation and Department of Interior. Some of laws have to be changed people that have water need to be able to lease their water. Please post!

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